"It's a big change," McIlroy told a pre-tournament press conference ahead of the WGC-Bridgestone Invitational at Firestone Country Club, where he won three years ago.

"JP has been a huge part of my life for the last decade.

"We started in July 2008 and went all the way to July this year, a lot of great times on and off the golf course. I still consider JP one of my best friends but sometimes to preserve a personal relationship you might have to sacrifice a professional one and that was sort of the decision I came to in the end.

"I was getting very hard on him on the golf course and I didn't want to treat him like that.

"It was a really tough decision to make but I thought, 'I'm coming to Firestone, I have four tournament rounds to get to know someone or get used to having someone else on my bag going into the last major of the year'.

"I thank JP for everything. He knows how much I think of him, what we've achieved together but at the end of the day it was a change I needed to make because I got to the point where if I didn't play a good shot or made a wrong decision I was getting more frustrated at him than I was at myself.

"I'd much rather be angry at myself for making a wrong decision than being angry at him."

Harry Diamond, the best man at McIlroy's wedding and a former top amateur player in his own right, will caddy for McIlroy at Firestone and in next week's US PGA at Quail Hollow.

It remains to be seen whether that arrangement will become permanent, but McIlroy did not rule out working with Fitzgerald again in the future.

"I hate the term fired, or sacked or axed because that's definitely not what it was," the Northern Irishman added. "I just changed my path a little bit but maybe in the future that path might come back to where it was."

McIlroy said it was a case of giving "credit where credit's due" after publicly praising Fitzgerald for helping him recover from five over par after six holes of the first round to finish fourth in the Open at Royal Birkdale.

But he was also visibly frustrated with a double bogey on the 10th in round three which effectively ended his chances of contending for the title.

''I should have hit a club to take all the bunkers out of play but hit a three iron which was the worst club," McIlroy said at the time. "It was a huge mental error."

Speaking at Firestone on Wednesday, McIlroy added: "Player-caddie relationships have their ups and downs and there was probably a few too many of those over the past year or so.

"I've been putting this line out there for a while that I'm trying to take ownership of my game a little bit more. I'm trying to take a little more responsibility.

"I don't think there was a certain moment at the Open, it was just a build-up of stuff that I felt like I needed to make that change.

"We did as well as we could. We maybe could have won a couple of more times, we probably want a couple of rounds back that got away from us, but I think we both walked away from at least the player-caddie relationship with our heads held high and really happy with what we've achieved together."

McIlroy won his first WGC event at Firestone Country Club in 2014 in between major triumphs in the Open at Royal Liverpool and the US PGA at Valhalla.

But he was unable to defend the WGC title due to an ankle injury suffered while playing football, and opted to contest the French Open last year when the two events clashed in a congested summer schedule caused by the Rio Olympics.

A rib injury suffered during equipment testing over the winter has restricted McIlroy to 11 events in 2017, but he has won twice at US PGA venue Quail Hollow and holds the course record at the venue.

"There's been decent results in there but decent results right now isn't good enough," he said of his season so far. "I'm expected to win and I expect more of myself also.

"With how I play around these courses it could, not save my season, but shoot me back into a place where I feel like I belong."